Ischemic Cerebral Blood Flow Research Articles

ARL 17477, a potent and selective neuronal NOS inhibitor decreases infarct volume after transient middle cerebral artery occlusion in rats.

We tested the effects of administration of a selective neuronal nitric oxide synthase (nNOS) inhibitor, ARL 17477, on ischemic cell damage and regional cerebral blood flow (rCBF), in rats subjected to transient (2 h) middle cerebral artery (MCA) occlusion and 166 h of reperfusion (n = 48) and in rats without MCA occlusion (n = 25), respectively. Animals were administered ARL 17477 (i.v.): 10 mg/kg; 1 mg/kg; 3mg/kg; N-nitro-L-arginine (L-NA) 10 mg/kg L-NA 1 mg/kg; and Vehicle. Administration of ARL 17477 1 mg/kg, 3 mg/kg and 10 mg/kg reduced ischemic infarct volume by 53 (p < 0.05), 23, and 6.5%, respectively. L-NA 1 mg/kg and 10 mg/kg increased infarct volume by 2 and 15%, respectively (p > 0.05). Administration of ARL 17477 (10 mg/kg) significantly (p < 0.05) decreased rCBF by 27 +/- 5.3 and 24 +/- 14.08% and cortical NOS activity by 86 +/- 14.9 and 91 +/- 8.9% at 10 min or 3 h, respectively, and did not alter mean arterial blood pressure (MABP). L-NA (10 mg/kg) significantly reduced rCBF by 23 +/- 9.8% and NOS activity by 81 +/- 7% and significantly (p < 0.05) increased MABP. Treatment with 3 mg/kg and 1 mg/kg ARL 17477 reduced rCBF by only 2.4 +/- 4.5 and 0%, respectively, even when NOS activity was reduced by 63 +/- 13.4 and 45 +/- 15.7% at 3 h, respectively, (p < 0.05). The data demonstrate that ARL 17477 inhibits nNOS in the rat brain and causes a dose-dependent reduction in infarct volume after transient MCA occlusion.

Calcitonin gene-related peptide reduces brain injury in a rat model of focal cerebral ischemia.

Calcitonin gene-related peptide is an endogenous vasodilating neuropeptide with a dense concentration in the trigeminocerebrovascular system. It is hypothesized that depletion of this peptide contributes to delayed cerebral ischemia after subarachnoid hemorrhage and that an exogenous supply of calcitonin gene-related peptide will augment ischemic cerebral blood flow and reduce neuronal injury. In this study we have investigated the effect of an intravenous infusion of calcitonin gene-related peptide (100 ng/kg per minute), started 1 hour before and continued throughout 4 hours of focal cerebral ischemia, on cerebral blood flow and the volume of brain injury in a rat model of middle cerebral artery occlusion. Calcitonin gene-related peptide produces a significant improvement in ischemic cerebral blood flow (32 +/- 2 compared with 13 +/- 2 mL/100 g per minute in the controls; t = 6.92, P < .0001) with a concomitant reduction in the volume of ischemic brain injury (102 +/- 22 compared with 234 +/- 19 mm3; t = 4.47, P < .001). These findings lend support for the potential use of this peptide in the prophylactic treatment of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage.

Pretreatment of transient focal cerebral ischemia in rats with the calcium antagonist AT877.

The efficacy of pretreatment with the recently developed intracellular calcium antagonist AT877 against transient focal cerebral ischemia was investigated in rats subjected to middle cerebral artery occlusion and reperfusion using the endovascular suture method. Halothane-induced moderate hypotension (60 mm Hg) was used during 100 minutes of temporary middle cerebral artery occlusion. In the treated animals (n = 10), an intravenous infusion of AT877 (0.03 mg/kg per minute) was initiated 30 minutes before the ischemic event and continued during the ischemic period. The control rats (n = 10) received physiological saline in a similar fashion. Local cerebral blood flow was measured by the hydrogen clearance technique. Neurological examinations were performed daily during the 48-hour observation period, and infarct size was assessed by triphenyltetrazolium chloride staining. A continuous infusion of AT877 significantly improved local cerebral blood flow during ischemia. The treated animals showed a better neurological outcome after a 24-hour observation period, and a significant reduction in ischemic brain injury resulted in both the neocortex (149 +/- 20 versus 41 +/- 14 mm3, P < .01) and the striatum (80 +/- 5 versus 46 +/- 8 mm3, P < .05). The size of the neocortical infarct was reduced, with increasing mean ischemic cerebral blood flow in the control and treated animals (r = .923, P = .0001). AT877 pretreatment was effective in preventing brain injury during transient focal cerebral ischemia and improving neurological status. This beneficial effect seems to be mediated, in part, by its primary action of increasing cerebral blood flow.

The effect of ritanserin, a 5-HT2 receptor antagonist, on ischemic cerebral blood flow and infarct volume in rat middle cerebral artery occlusion.

In a previous study from our laboratory, ritanserin, a specific 5-HT2 serotonin receptor antagonist, reduced ischemic damage in the setting of transient global ischemia. In this study, we examined the effect of ritanserin on ischemic cerebral blood flow, systemic blood pressure, and infarct volume in the model of permanent focal ischemia with brain temperature controlled at 35.0 degrees C to 36.0 degrees C. Thirty-seven male Sprague-Dawley rats were used. The right middle cerebral artery was permanently occluded. Ritanserin (8 mg/kg) or vehicle was continuously administered intravenously for 90 minutes starting 10 minutes after middle cerebral artery occlusion. Cerebral blood flow was monitored by laser Doppler flowmetry in the ischemic cortex before and for 2 hours after arterial occlusion. Brains were perfusion-fixed 3 days later, and infarct volumes were measured. Mean arterial blood pressure was not affected by treatment. In the vehicle and ritanserin groups, mean ischemic cerebral blood flow (percent of preischemic values) was 34.6 +/- 14.7% (mean +/- SD) and 26.6 +/- 15.0%, respectively. Hemispheric infarct volumes were 119.3 +/- 49.4 mm3 and 136.6 +/- 49.6 mm3, respectively. No significant differences were recognized. Intravenous administration of ritanserin did not affect mean arterial blood pressure or cerebral blood flow in the ischemic region during the acute phase of ischemia. No protective effect of ritanserin was apparent in the setting of permanent focal ischemia when treatment was begun shortly after the onset of ischemia.

Efficacious experimental stroke treatment with high-dose methylprednisolone.

Recent studies reveal success in treating spinal cord trauma with early, high-dose methylprednisolone. As in spinal cord research, failure to find therapeutic effects with steroids in studies of acute stroke treatment may reflect institution of treatment too late and at too low dosage. We presently test the efficacy of stroke treatment with methylprednisolone administered early and at high doses using a cat temporary middle cerebral artery occlusion model. We occluded the middle cerebral artery for 4 hours in 24 pentobarbital-anesthetized cats. To enhance the probability of brain injury, we maintained the cats' serum glucose concentrations at high levels both during occlusion and for 6 hours afterward. Using a blinded, randomized study design, we treated 12 cats with methylprednisolone (30 mg/kg IV infused over 15 minutes starting 30 minutes after occlusion followed by 5.4 mg.kg-1.h-1 IV for the next 23 hours) and 12 control cats with vehicle. During and for 8 hours after occlusion, we monitored cerebral blood flow, brain and rectal temperatures, and multiple cardiovascular and blood compositional parameters. We assessed brain pathological outcome after animal survival for 4 days or after acute death from hemispheric edema. Experimental and control animals showed similar early mortality rates (treated, 3/12; controls, 4/12). However, surviving methylprednisolone-treated cats (n = 9) showed a mean infarct size more than six times smaller than in the control animals (n = 8) (mean +/- SEM, 2.4 +/- 0.7% versus 15.6 +/- 6.2% of the ischemic territory, respectively; P < .05). The methylprednisolone-treated animals also showed less marked reduction in cerebral blood flow during ischemia than did the controls (mean +/- SEM, 58 +/- 5% versus 74 +/- 4%; P < .005). Administering methylprednisolone at high doses early after onset of ischemia significantly reduces tissue injury in cats that survive 4 days of temporary middle cerebral artery occlusion. This improvement in outcome occurs in the setting of significant increases in ischemic cerebral blood flow. However, methylprednisolone treatment did not reduce hemispheric edema in animals that died early after temporary middle cerebral artery occlusion.

Effect of the kappa-1 opioid agonist CI-977 on ischemic brain damage and cerebral blood flow after middle cerebral artery occlusion in the rat

The effects of the kappa-1 opioid agonist CI-977 upon the volume of ischemic brain damage (defined using quantitative neuropathology) and local cerebral blood flow (CBF) (defined using quantitative [ 14C]iodoantipyrine autoradiography) have been examined at 4 h and 30 min, respectively, after permanent middle cerebral artery (MCA) occlusion in halothane-anesthetised rats. Treatment with CI-977 (0.3 mg/kg, s.c.) 30 min before and 30 min after occlusion of the MCA reduced the volume of infarction in the cerebral hemisphere (reduced by 27% when compared to vehicle;P<0.05) and cerebral cortex (reduced by 32%;P<0.05), despite a marked and sustained hypotension, with only minimal effect on damage in the caudate nucleus. In the hemisphere contralateral to the occluded MCA, treatment with CI-977 (0.3 mg/kg, s.c.) 30 min prior to the induction of ischemia failed to demonstrate any significant effect on either the level of local CBF in any of the 25 regions examined or on the volume of low CBF determined by frequency distribution analysis. In the hemisphere ipsilateral to MCA occlusion, CI-977 failed to produce statistically significant alterations in either the level of local CBF in 23 of the 25 regions or on the volume of low CBF, but areas of hyperemia were observed in both the medial caudate nucleus and lateral thalamus (local CBF increased by 65% and 86%, respectively, when compared to vehicle). The results of the present study indicate that the kappa-1 opioid agonist CI-977 is neuroprotective in a rat model of focal cerebral ischemia where key physiological variables have been assessed throughout the entire post-ischemic period, and fail to demonstrate that the neuroprotective effects of CI-977 in this model are due to improved blood flow to ischemic tissue.

Ischemia-induced changes in brain monoamine metabolism in aged spontaneously hypertensive rats.

Effects of aging on monoamine metabolism in transient cerebral ischemia were studied using adult and aged female spontaneously hypertensive rats (SHRs). Tissue monoamine contents in discrete brain areas were quantified after 20 min of cerebral ischemia with or without 30-min recirculation. Cerebral blood flow (CBF) was determined with a hydrogen clearance method in separate experiments. Dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) contents in the striatum, nucleus accumbens and septum decreased in ischemic aged SHRs, compared with those in ischemic adult SHRs. After 30-min recirculation, DA contents were actually unchanged with inconsistently increased DOPAC levels. Ischemic CBF decreased to < 20% of the resting CBF in the striatum and cortex, which was not different between the two age groups of SHRs. These results indicate that aging is primarily responsible for more severely impaired DA metabolism during cerebral ischemia in aged SHRs.

Hydroxyethyl starch 200/0.5 reduces infarct volume after embolic stroke in rats.

We evaluated isovolumic hemodilution with hydroxyethyl starch 200/0.5 in a rat model of focal cerebral ischemia. This compound avoids the unfavorable viscosity and erythrocyte aggregation abnormalities of low molecular weight dextran during administration over a period of several days. Sprague-Dawley rats, anesthetized with 0.5-1% halothane and 70% N2O, were subjected to silicon cylinder (treated and control groups) or sham (sham group) embolization of the cerebral circulation. Thirty minutes after embolization, the treated group (n = 5) was infused with 11 ml/kg of 10% hydroxyethyl starch 200/0.5, and the control (n = 5) and sham (n = 4) groups were infused with saline for 1 hour. In the treated group, 7.1 ml/kg of blood was withdrawn. After 24 hours, the animals were reanesthetized, and cerebral blood flow was determined with [14C]iodoantipyrine. Alternative brain slices were either incubated with 2,3,5-triphenyltetrazolium chloride for infarct volume determination or frozen for ischemic volume and cerebral blood flow determination using autoradiography. The hematocrit in the treated group was reduced from (mean +/- SEM) 46 +/- 1% to 35 +/- 2% at 1.5 hours (p < 0.01). Cortical blood flow was within the normal range of 115-185 ml/min/100 g, except for the ischemic cortex in the embolized groups, treated and control. The ischemic and infarct volume of the treated group was reduced by 74% (p < 0.05) and 89% (p < 0.05), respectively, from the control group. The treated and sham ischemic and infarct volumes were not statistically different. These data suggest that hydroxyethyl starch 200/0.5 could be an effective treatment for ischemic stroke when administered early, because it reduces infarct and ischemic volumes from control values to levels indistinguishable from those of the sham group.

Age-related vulnerability to cerebral ischemia in spontaneously hypertensive rats.

We sought to determine the effects of aging on regional cerebral blood flow and ischemic brain damage in transient cerebral ischemia in rats. Five adult (5-6 months) and five aged (18-22 months) female spontaneously hypertensive rats were subjected to 20 minutes of bilateral carotid occlusion and 60 minutes of recirculation under amobarbital anesthesia (100 mg/kg i.p.). Regional cerebral blood flow in the hippocampus and striatum was measured using the hydrogen clearance method. Nine adult and 14 aged rats were subjected to 20 minutes of bilateral carotid occlusion or were sham-operated under ether anesthesia. Seven days after 20 minutes of cerebral ischemia, the rats' brains were perfusion fixed. Ischemic damage in the hippocampus and striatum was graded (0 [normal] to 3 [majority of neurons damaged]). After 20 minutes of bilateral carotid occlusion, striatal cerebral blood flow decreased to 9.1 +/- 1.5 and 3.9 +/- 2.0 ml/100 g/min in aged and adult rats, respectively, and hippocampal cerebral blood flow decreased to 8.6 +/- 2.4 and 5.7 +/- 2.4 in aged and adult rats, respectively. Although these ischemic cerebral blood flow values were not significantly different between the two age groups, scores for ischemic damage in the hippocampus CA-1 subfield and striatum were significantly higher in aged than in adult rats (p less than 0.05, Kruskal-Wallis' h test with Bonferroni correction). We conclude that aging may be a primary factor in the development of greater ischemic neuronal damage observed in aged hypertensive rats.

Improvement of Ischemic Symptoms and Cerebral Blood Flow after Percutaneous Transluminal Angioplasty for Renovascular Hypertension

A 53-year-old male complained of frequent left motor-sensory transient ischemic attack for 4 months. On admission, he demonstrated mild right hemiparesis, dysarthria, and right hemisensory disturbance of all modalities. Cerebral angiography demonstrated complete occlusion of the left internal carotid artery just above the origin of the ophthalmic artery and a stenotic lesion at the horizontal segment of the right middle cerebral artery. Renal angiography showed severe stenosis of the right renal artery. Systolic blood pressure was over 200 mmHg and marked circadian variation of blood pressure was noted. Serum renin was 4.0 ng/ml/hr. Four months after superficial temporal artery-middle cerebral artery anastomosis, left carotid angiography showed good patency of the bypass and the ischemic symptoms completely disappeared. Single photon emission computed tomography (SPECT) showed increased cerebral blood flow (CBF), especially in the left hemisphere after surgery. Six months after the bypass surgery, he complained of mild right hemiparesis again. Shortly after percutaneous transluminal angioplasty (PTA) for renal arterial stenosis, his hemiparesis was improved and the systolic blood pressure stabilized to 150-170 mmHg. SPECT showed the CBF had also recovered in both hemispheres. The improvement in ischemic symptoms and increased CBF after PTA were probably related to stabilization of the systemic blood pressure or inhibition of serum renin-angiotensin.